Carbon nanotubes 'cloned' by USC researchers

SAN FRANCISCO—A team of researchers at the University of Southern California (USC) and the National Institute of Standards and Technology (NIST) in Maryland say they have overcome a key hurdle to carbon nanotube manufacturing by inventing a system that consistently produces carbon nanotubes of a predictable diameter and symmetry.

Carbon nanotube transistors—first built by researchers at Delft University in 1998—are widely expected to one day replace silicon transistors in computers and other electronics. Carbon nanotubes have the potential to be far smaller, faster and consume less power than silicon transistors.

But carbon nanotube transistors are difficult to manufacture in a predictable way. Scientists have had a difficult time controlling the manufacture of nanotubes to the correct diameter, type and chirality— a property of asymmetry. All of these factors are critical to controlling nanotubes' electrical and mechanical properties.

Carbon nanotubes are grown using a chemical vapor deposition (CVD) system in which a chemical-laced gas is pumped into a chamber containing substrates with metal catalyst nanoparticles, upon which the nanotubes grow. It is generally believed that the diameters of the nanotubes are determined by the size of the catalytic metal nanoparticles. But attempts to control the catalysts in hopes of achieving chirality-controlled nanotube growth have been unsuccessful.

Chongwu Zhou holds up a piece of plastic substrate used to build nanoscale transistors and circuits.

Credit: USC

The USC team—led by Professor Chongwu Zhou of the USC Viterbi School of Engineering and Ming Zheng of NIST—jettisoned the catalyst and instead planted pieces of carbon nanotubes that had been separated and pre-selected based on chirality, using a nanotube separation technique developed and perfected by Zheng and his coworkers at NIST. Using those pieces as seeds, the team used chemical vapor deposition to extend the seeds to get much longer nanotubes, which were shown to have the same chirality as the seeds.

The process is referred to as "nanotube cloning." The USC team will next carefully study the mechanism of the nanotube growth in this system to scale up the cloning process to get large quantities of chirality-controlled nanotubes and use those nanotubes for electronic applications.

"Controlling the chirality of carbon nanotubes has been a dream for many researchers. Now the dream has come true," Zhou said. The team has already patented its innovation, and its research was published last week in the journal Nature Communications.

In addition to Zhou and Zheng, the research team on this project included Jia Liu, Chuan Wang, Bilu Liu and Liang Chen of USC and Xiaomin Tu of NIST. Funding for the project was provided by the Semiconductor Research Corp.'s Focus Research Program Functional Engineered Nano Architectonics center and the Office of Naval Research.